Conspiracy theory: The global dissemination of genetically modified foods by Monsanto Inc. is part of a secret program, called Agenda 21, launched by the Rockefeller and Ford foundations to shrink the world's population.

No one wants to be pegged as "conspiracy nut," but a recent study from the University of Chicago suggests that more people than you might expect actually buy into some out-there theories.

A survey that asked Americans how they feel about six medical conspiracy theories found that such misconceptions are fairly common and do affect the medical decisions of people who believe them, according to an article posted in JAMA Internal Medicine.

Possibly the most widely known conspiracy theory is the notion that vaccinations given to children might cause psychological disorders and autism, a theory made more popular by celebrities such as Jenny McCarthy.

The study found that 69 percent of Americans have heard of the vaccination theory and, despite massive public relations efforts to dispel the myth, 20 percent of those surveyed believe it to be true.

The study found that people who were more likely to be "high conspiracists" were also more likely to avoid traditional medicine, use herbal supplements and buy organic food.

Click through the slideshow to see the results for each of the six conspiracy theories used in the study.